There have been several different types of optical light pipes developed in the past. In general, these prior art light pipes either emit light out of the end of the light pipe or emit light across the entire surface of the light pipe.
Orcutt, U.S. Pat. No. 4,422,719, discloses a light pipe with a translucent coating over a core material which allows the light which is transmitted axially to be dispersed radially around the light pipe. This translucent layer causes multiple random reflections which causes the entire width of the light pipe to be illuminated.
In U.S. Pat. No. 4,466,697, by Daniel, another type of construction of light pipe is disclosed. This light pipe consists of an extruded material and deposited within that material are co-extruded reflective particles. These particles randomly reflect the light and again as in Orcutt, there is no pattern to the light distribution. The light emitted from this prior art light pipe is also totally random and consequently the entire light pipe is illuminated.
In U.S. Pat. No. 4,195,907, Zamja, et al., there is disclosed an extruded optical fiber which contains dispersed air bubbles co-extruded within the fiber. These air bubbles inherently have a different index of refraction than that of the surrounding material thus they provide reflective surfaces similar to what is attained in Daniel with his reflective particles. Zamja's light pipe, as in Daniel, utilizes reflective surfaces that are randomly aligned and are not oriented in any manner. Because of the random orientation of the reflective surfaces, the reflection of the light transmitted axially down the fiber is also random and consequently the entire fiber is illuminated.
In U.S. Pat. No. 3,535,018, Vasilatos, there is disclosed an optical fiber which has notches cut into the fiber in order to provide reflective surfaces. These notches are positioned in a random manner and consequently there is no orientation of the emitted light coming from the fiber. Again, as in Daniel and Zamja, this causes the entire fiber to be illuminated across its entire width.
U.S. Pat. No. 5,671,306 describes a lighting structure for intensely illuminating a narrow linear region through a longitudinal slit in a lightguide. The lightguide has a reflective internal surface and a lens mounted in a slit shaped aperture. The lens includes a plurality of parallel planar prisms for directing light out of the lightguide, however, light is emitted only from the longitudinal slit in this device. Due to the planar construction of the parallel prisms the emitted light is in a single radial direction.
Considerable prior art may be seen in several U.S. patents to Whitehead, starting with U.S. Pat. No. 4,260,220. There are several design features which repeat in the Whitehead prior art. In Whitehead's light pipes, the light pipes are primarily designed to efficiently transmit light down the light pipe with minimal losses. This is achieved by constructing a light pipe from a sheet of material containing prismatic surfaces which are aligned parallel to the axis of the light pipe. These features reflect and redirect the axially transmitted light by explotation of the principal of total internal reflection. Whitehead describes these prismatic surfaces as being in octature due to their construction consisting of a series of 90 degree prism faces which face each other. The light pipes in Whitehead go to great lengths to achieve near 100% efficient transmission of the axially transmitted light. In order to achieve this the prismatic elements are designed to reflect as much light as possible and not to redirect and transmit it, as in my invention. In U.S. Pat. No. 5,481,637, Whitehead discloses a light source reflector for a diffuse light source located within another light pipe. This reflector is constructed with prismatic surfaces aligned perpendicular to both the axis of the light pipe and the axis of the light source, but as in his other designs, the prismatic surfaces are utilized for efficient reflection within the light pipe not transmission of the light radially out of the light pipe. In addition, in U.S. Pat. No. 5,481,637 the prismatic reflector surrounds a diffuse light source which is a fluorescent type light source. The purpose of the prismatic reflector is to reflect the diffuse light rays from the light source light down the axis of the light pipe and prevent any radial emission of light. As before, the prismatic surfaces are in octature in order to efficiently reflect the light and prevent any light from passing radially through the prismatic surfaces of the light pipe.
In all of the Whitehead prior art no reference is made to the appearance of the light emitted from the light pipe. Whitehead is primarily concerned just with the efficient axial transportation of light not it's distribution or appearance to a observer.
Another prior art device described in U.S. Pat. No. 4,906,070 to Cobb, Jr. incorporates prismatic features utilizing prismatic films. These devices utilize prismatic films contained in a box, tube, or other housing in order to support and orient the film.
The prior art devices whether they are described as optical fibers, light pipes, lighting structures, or luminaries are generally designed to emit diffuse light across the entire width of the emitting area of the device. This diffuse, non-oriented emitted light results in the entire width of the emitting area being illuminated when viewed by an observer. Other prior art devices are designed to transmit light down a tube without emitting light from the sides of the tube.
Prior art manufacturing methods such as machining or sandblasting features in optical elements, results in surfaces that create diffuse emitted light and do not achieve highly efficient, specular, radial emission of light.
The present invention, on the other hand, consists of an optical light pipe with oriented prism surfaces which provide specular emission of light. These prism surfaces are oriented generally perpendicular to the axis of the light pipe. These prism surfaces act in conjunction with another media, with a different index of refraction such as air, to cause the axially directed light from the light source to be redirected out to the sides. Because of the controlled orientation of the prisms and the controlled manner in which the light is axially directed down the light pipe, there is a plane of light that is visible to an observer. This plane of light appears as a very narrow line of light much smaller than the width of the prismatic surfaces of the light pipe. Because this narrow, very intense plane of emitted light is visible to the observer, this light appears as if it is a highly collimated axially transmitted beam of light from the light source. Due to the curvature of the prismatic surfaces, only this plane of light which appears to be at the center of the light pipe is apparent to the observer. This gives the observer the impression that the light from the light pipe is emitted axially within the light pipe, not radially from the surface, as is actually the case. It is this phenomenon that gives the invention the appearance of a laser beam transmitted through a medium inside the light pipe. The uniform intensity and width of this line of light is an indicator of the optical efficiency of the light pipe in distributing light radially along its length.